In many cases, a torque converter is provided with a lock-up device for directly transmitting torque from a front cover to a turbine. The lock-up device includes a piston that can be frictionally coupled to the front cover, a drive plate fixed to the piston, a plurality of torsion springs supported by the drive plate, and a driven plate elastically coupled to the piston and the drive plate by the plural torsion springs in the rotational direction. The driven plate is fixed to the turbine.
Further, as described in Japanese Laid-open Patent Application Publication No. JP-A-2010-48291, a lock-up device of a so-called multi-plate type using a plurality of clutch plates has been also proposed for increasing the clutch capacity of the lock-up device.
When torque is herein transmitted by the lock-up device, reduction in stiffness and expansion in a torsional angle are required for the torsion springs to effectively absorb and attenuate variation in torque inputted thereto from an engine. In view of this, as described in Japanese Laid-open Patent Application Publication No. JP-A-2002-89657, a device has been proposed that pairs of torsion springs among a plurality of torsion springs composing a part of a damper mechanism are configured to act in series through an intermediate member.